1. Field of the Invention
The present invention relates to a sample dispensing apparatus for dispensing a liquid sample, such as blood and urine, and an automatic analyzer using the sample dispensing apparatus. More particularly, the present invention relates to a sample dispensing apparatus with a function of enabling clogging of a suction/ejection nozzle to be detected with high accuracy, and an automatic analyzer using the sample dispensing apparatus.
2. Description of the Related Art
An automatic analyzer, such as a biochemical automatic analyzer or an immune automatic analyzer, includes a sample dispensing apparatus for automatically sucking and ejecting (hereinafter referred to as “dispensing”) a liquid sample from a sample vessel from and into a reaction vessel.
Conventionally, the sample dispensing apparatus comprises a sample probe, a dispensing syringe connected to the sample probe, and a mechanism for moving the sample probe to a predetermined position. The sample dispensing apparatus repeats a dispensing operation as follows. A fore end of the sample probe is inserted in a sample, and the dispensing syringe is driven to move over a predetermined distance to suck a predetermined amount of sample. Then, the sample probe is moved to the reaction vessel into which the sucked sample is ejected.
In sample tests such as biochemical tests, blood serum and plasma are employed as samples in many cases. If these samples are left to stand for a long time from sampling to inspection, a solid (hereinafter referred to as a clot), e.g., fibrin, is generated in the sample. Then, if such a sample is put, as it is, in an automatic analyzer, the sample probe may clog with the generated clot. Upon the clogging of the sample probe, a predetermined amount of sample cannot be dispensed to the reaction vessel and an accurate analysis result can no longer be obtained. This results in a great loss of analysis reliability in the automatic analyzer.
To overcome the disadvantage described above, many proposals have been made with the concept of providing a pressure sensor in a dispensing flow passage including the sample probe, and detecting the clogging of the sample probe based on detected pressure fluctuations. Japanese Unexamined Patent Application Publication No. 7-198726 pays attention to a second derivative value of a waveform of the pressure fluctuations and states that abnormal suction can be detected by comparing the second derivative value with a threshold (hereinafter referred to as “first related art”). Also, Japanese Unexamined Patent Application Publication No. 11-83868 pays attention to a pressure remaining on the negative side after the end of the sucking operation and it compares the remaining pressure with a threshold to determine the occurrence of clogging when the remaining pressure is lower than the threshold (hereinafter referred to as “second related art”). Further, Japanese Unexamined Patent Application Publication No. 2000-39440 discloses a technique of comparing an area value, which is obtained by integrating an output of a pressure sensor, with a preset reference value and determining an abnormality in the sample dispensing operation (hereinafter referred to as “third related art”).